Circuit breaker releasing mechanism



March 13, 1934. Q HQDGKINS 1,951,243

CIRCUIT BREAKER RELEASING MECHANISM Filed Jan. 17, 1935 CURRENT CURRENTINVENTOR CHARLES H. HODGKINS BY HIS ATTORNEYS Patented-Mar. 13, 1934PATENT OFFICE 1,951,243 CIRCUIT BREAKER RELEASING MECHANISM Charles H.Hodgkins, Fairfield, Conn, assignor to The Bryant Electric Company,Conn., a corporation of Connecticut Bridgeport,

Application January 11,1933, Serial No. 652,225

12 claims.

This invention relates to current-responsive means for causing theopening of a circuit breaker upon the occurrence of predeterminedcurrent conditions in the circuit controlled by the circuit breaker.More particularly this invention relates to a circuit breaker releasingmeans embodying more than one bimetallic element, which elements arecaused to flex upon the occurrence of excess current, and one of whichcontrols a varying of the rate of flexure, upon occurrence of apredetermined excess of current.

My inventionis particularly useful when it is desired to change theoverload time trip characteristics of circuit breakers which haveoverload tripping means which are responsive to thermal conditions inacircuit. My invention may 'be applied to existing switches; or it may beincorporated into switches during their manufacture to avoid thenecessity of carrying in stock a large number of thermal elements eachhav-.

ing a different characteristic, as has been done in the past when it hasbeen desired to have v switches which opened at different currentvalues.

It is an object of this invention to provide a releasing mechanism forcircuit breakers, the characteristics of which mechanism will changeupon the occurrence oi. a predetermined current value in the circuit,whereby the opening of the circuit breaker may be hastened or retarded.

Another object is to provide means, applicable to thermally-actuabletripping means for circuit breakers, for changing the characteristics ofthe tripping means.

Another object is to provide means applicable to thermally-actuabletripping means for circuit breakers, for increasing or decreasing thetime lag between occurrence of an overload condition and tripping of thecircuit breaker.

Other objects and advantages of this invention will be described inconnection with the accompanying drawing.

In the drawing:-

Figure 1 illustrates diagrammatically a circuit breaker controlled by atripping mechanism in which the time lag is decreased for high currentvalues; a

Figure 2 is a graph showing a typical curve resulting from the inventionas shown in Figure 1;

Figure 3 illustrates diagrammatically a circuit breaker controlled byanother form of tripping mechanism in which the time lag is increased;and

Figure 4 is a graph showing a typical curve resulting from the inventionshown in Figure 3.

Referringto the drawing a switch lever 10 pivotally mounted at 12 isnormally biased to opencircuit position by a spring 14 but is held inclosedcircuit position by a thermally responsive bimetallic element 16mounted at one end upon a stationary support 18 but having its other endfreeto flex in a well known manner as the element is subjected to anincreased temperature. A contact 20 is mounted upon and insulated fromthe switch lever 10 and connected by a conductor 22 to a source ofpower. The contact 20 while in closed circuit position of the circuitbreaker engages afixed contact 24 suitably mounted upon a stationarysupport 26 and connected by a conductor 28 to one end 29 of a resistanceunit forming a heater element 30 which is positioned adjacent to but nottouching the bimetallic element 16 in order that the heat generated maycause heating of the bimetallic element; The other end 31 of the heaterelement may be connected to an electric motor 32 or other translatingde- 76 vice which is also connected to the source 01 .power by aconductor 34, The construction as thus far described is well known inthe art. In operation, when the element 16 is sufllciently heated itwill bend down away from the lever 80 10 releasing the lever which willthen snap away from contact 24 under the influence of spring 14.

In order to decrease the time taken to open the circuit breaker a fixedcontact 40 is connected to the heater element 30 at some point interme-86 diate its ends 29 and 31. The exact point of connection of thecontact 40 to the heater element 30 will be determined by the decreasein time lag which is desired. The contact 40 is normally engaged by amovable contact 42 mounted upon a 90 bimetallic element 44 which in turnis mounted at one end upon a fixed support 46. The bimetallic element 44is placed adjacent to, but not touching, the heater element 30 in orderthat upon the occurrence of a rise in temperature of the heater element30 the bimetallic element 44 may be caused to flex away from the contact40. A conductor 48 connects the fixed end of the bimetallic element 44with one end of the heater element 30.

The bimetallic element 44 is constructedto flex more, upon a less degreeof heat, than the bimetallic element 16 in order to separate thecontacts 42 and 40 upon the generation of a less degree of heat than isrequired to cause sufllcient flexing of the bimetallic element 16 toopen the switch. By reason of this construction of the bimetallicelement the current which is normally shunted through the auxiliarybimetallic element 44 is caused to go through the whole of the heaterelement 30. Since the current remains substantially the same even thoughthe whole heater 30 is placed in the circuit it will be obvious that anincrease in the amount of heat will result from the full currenttraversing the whole of the heater element 30. As a result of thisincrease in heat, the bimetallic element 16 will be caused to flex morerapidly and to a greater extent and will thereby more quickly permit theseparation of the switch contacts 22 and 24 under the influence ofspring 14. Referring to Figure 2, the typical curve shown therein isplotted against current and time. The break in the curve indicates thevalue at which the shunt is removed from the heater element.

Referring now to Figures 3 and 4 it will be noted that the switch,bimetallic trip 16, heater, motor and connections therebetween areillustrated as in Figure 1 and therefore it will not be necessary toagain describe this construction. The construction shown in Figure 3differs from that shown in Figure 1 in the respect that amovable'contact 52, which is located upon one end of an auxiliarybimetallic element 54 whose other end is mounted upon a fixed support56, is normally disengaged from the fixed contact which is connectedintermediate the ends 31 and 29 of the heater element 30. In this formas in the form of Figure 1, the fixed end of the auxiliary bimetallicelement is connected with one end of the heater element 30. Theauxiliary bimetallic element 54 is constructed so as to flex towardcontact 50 upon less amount of heat than is required for the bimetallicelement 16 to bend and release the switch arm 10. Thus the contact 52.will'engage the contact 50 and form a shunt around a portion of theheater element 30 thereby reducing the amount of heat generated in theelement 30 and consequently retarding the flexing of the bimetallicelement 16. Thus the time taken for the separation of the switchcontacts 22 and 24 will be increased. Figure 4 shows the typical curveof the Figure 3 combination, in which the current is plotted againsttime. The break in the curve indicates the value at which a portion ofthe heater element is shunted. It will be noted that this break proceedsin the opposite direction from the break shown in Figure 2, because inthe Figure 3 combination the time lag is increased'while in the Figure 1combination the time lag is decreased.

The contact 42 is preferably mounted upon a leaf spring 43 in order forit to have firm engagement with the stationary contact 40 withoutplacing the thermo-bar 16 under unnecessary strain, and in order toavoid the necessity of fine adjustments of the thermo-bar to get a firmcontact without exerting unnecessary strain on the thermo-bar.

From the foregoing it will be apparent that I" have provided a simpleand effective way of varying the tripping value of mechanism for openingcircuit breakers upon the occurrence of overload conditions.

Modifications and changes within the scope of my invention will occurto'those skilled in the art. Therefore I have shown my inventiondiagrammatically and do not limit myself to the exact form illustrated.

I claim:-

1. An overload tripping means for a circuit breaker comprising aplurality of heat responsive devices, means energized by current in thecircuit to be controlled and associated with said devices for subjectingthem to the thermal e le t ofoverload current in said circuit, one ofsaid devices being movable to cause tripping of the circuit breaker uponoverload, another of said devices being movable upon a less overloadthan said tripping device to vary the thermal effect of the current uponsaid tripping device.

2. An overload tripping means for a circuit breaker comprising apluralityof heat responsive devices, means energized by current in thecircuit to be controlled and associated with said devices for subjectingthem to the thermal effect of overload current in said circuit, one ofsaid devices being movable to cause tripping of the circuit breaker uponoverload, another of said devices being movable upon a less overloadthan said tripping device to increase the thermal effect of the currentupon said tripping device.

3. An overload tripping means for a circuit breaker comprising aplurality of heat responsive devices, means energized by current in thecircuit to be controlled and associated with said devices for subjectingthem to the thermal effect of overload current in said circuit, one ofsaid devices being movable to cause tripping of-the circuit breaker uponoverload, another of said devices being movable upon a less overloadthan said tripping device to decrease the thermal effect of the currentupon said tripping device;

4. An overload tripping device for circuit breakers comprising aplurality of thermally responsive means one of which is movable onoverload to cause tripping of the circuit breaker, current responsiveheat-generating means associated with said thermally responsive means,and means controlled by'one of said thermally responsive means to varythe amount of-heat generated in said heat-generating means upon theoccurrence of a predetermined-current in said heat generating means.

5. An overload tripping device for circuit breakers comprising aplurality of thermally responsive elements, current responsive heatgenerating means associated with said elements, one of said elementsbeing movable to,cause tripping of the circuit breaker on overload, theother of said elements opening a shunt circuit around a part of saidheating device upon the occurrence of a predetermined current in theheating device for increasing the amount of heat generated.

6. An overload tripping device for circuit breakers comprising aplurality of thermally responsive elements, current responsiveheat-generating means associated with said elements, one of saidelements being movable to cause tripping of the circuit breaker, theother of said elements closing a shunt circuit around a part of saidheating means upon the occurrence of a predetermined current in theheating means for decreasing the amount of heat generated.

7. An overload tripping device for circuit breakers comprising aplurality of thermally responsive elements of different characteristics,a heater element adjacent said thermally responsive elements and meanscontrolled by one oi said thermally responsive elements shunting a isponsive elements of different characteristics, a

heater element for causing bending of said elements, one of saidelements holding a switch in closed circuit position, the other of saidelements controlling a shunt circuit for varying upon cur ence of apredetermined current therein the amount of heat generated insaid-heater element.

9. An overload tripping device for circuit breakers comprising abimetallic latching device controlling the opening movement of thecircuit breaker, a bimetallic switch, and a current operated heater forsaid bimetallic members, said bimetallic switch closing a shunt circuitaround a portion of said heater upon the occurrence of a predeterminedoverload of less magnitude than that required'to operate the latchingdevice.

10. An overload tripping device for circuit breakers comprising abimetallic latching device controlling the opening movement of thecircuit breaker, a bimetallic switch, and a current operated heater forsaid bimetallic members, said bimetallic switch opening a shunt circuitaround a portion of, said heater upon the occurrence of a predeterminedoverload of less magnitude than that required to operate the latchingdevice.

11. An overload tripping means for a circuit breaker comprising a heatresponsive device, means associated with said device for subjecting itto thermal effect of overload current in a circuit, said device beingmovable to cause tripping of the circuit breaker upon overload, and acurrent-responsive device movable upon a less overload than saidtripping device to vary the thermal effect of the current upon saidtripping device.

12. An overload tripping means for a circuit breaker comprising a heatresponsive device, means associated with said device for subjecting itto thermal effect of overload current in a circuit, said device beingmovable to cause tripping of the circuit breaker upon overload, and acurrent-responsive device movable upon a less overload than saidtripping device to decrease the thermal efiect of the current upon saidtripping device.

CHARLES H. HODGKINS.

